Great Wicomico Study

environmental stressors that predispose fish to development of lesions in the
Great Wicomico River (GWR). The Pfiesteria Initiative Ecological Study (PIES) is
an integrated, comprehensive field investigation of watershed and riverine
processes and their relationship to environmental stressors.

Menhaden are intensively sampled from spring through fall to determine
temporal and spatial variations in lesion prevalence. Histological and
microbiological studies are performed to identify pathogens associated with
lesions.

Physical and water quality parameters in feeder streams, groundwater, and the
river are studied to determine how the watershed and groundwater influence
nutrient and plankton dynamics in the river and development of hypoxic/anoxic
conditions.

Water samples are collected and processed for determination of abundance and
culture of heterotrophic dinoflagellates such as Pfiesteria and pathogens such
as Aphanomyces.

Most fish kills occur as a result of hypoxia or low dissolved oxygen,
especially for such aerobically active fish as menhaden. Unresolved fish kills
are examined for a suite of potential causes.

Hydrodynamic and watershed models are in development to allow prediction of
water quality, nutrient concentrations, and occurrence of environmental
stressors in the GWR.